EarthTalk: What, if anything, fills the empty
space underground created by the extraction of billions
of gallons of oil? Could oil drilling be one of the causes
of increasing amounts of land settling and sinkholes in
oil rich areas? Can it cause earthquakes?
-- Linda Anderson, Sedona, AZ
U.S. Geological Survey cites several cases throughout
the 20th century which they say demonstrate how accelerated
withdrawal of oil and gas from some reservoirs can
lower land elevation, cause minor earthquakes and
activate faults around oil fields.
© Richard Masoner, courtesy Flickr
crude oil (and natural gas) we drill for the world over
is, for the most part, stored in tiny pores within rock
up to only about three miles deep in the Earth‘s hugely
dense crust. At such depths, the oil there is under fairly
high pressure. When it is removed, other liquids—usually
water—move in to take its place, equalizing the pressure
in the process. Sometimes oil extractors pump water into
one side of an oil field to push oil toward wells on the
other side, and the water replaces the oil accordingly.
cases where other liquids don‘t move in, such as in
the North Sea off The Netherlands, the porous rock layer
that harbored the oil originally can collapse after extraction,
causing slight amounts of land settling (known as “land
subsidence”) in the rock layer surfaces above, but
typically no more than a few tenths of an inch per year.
in the U.S., land subsidence induced by the large volume
extraction of underground resources including oil and gas
“is more common than most people realize,” according
to the U.S. Geological Survey (USGS), a government agency
which collects, monitors, analyzes and provides scientific
understanding about natural resource conditions, issues
and problems. Flat coastal plains and wetlands near sea
level are most at risk from this potential side effect.
ground water pumping, not oil or gas extraction, is the
single largest source of land subsidence, says the USGS,
but the agency cites several cases throughout the 20th century
which they say demonstrate how “accelerated withdrawal
of oil, gas and associated water from shallow unconsolidated
reservoirs could lower the land elevation, cause minor earthquakes,
and activate faults [around oil fields].”
around large, mature oil and gas fields that coincide with
faults could add enough stress to trigger small, locally
based earthquakes as far as two kilometers away from the
offending wells. Most geologists agree, though, that it
is unlikely that oil and gas extraction could contribute
to or cause major earthquakes, which are generated at depths
far deeper than would be practical to drill for oil or gas.
The USGS does suggest, however, that the continued withdrawal
of oil and gas and the associated decline in underground
fluid pressure could even contribute to coastal sea level
rises by lowering coastal land elevations.
for sinkholes, modern oil wells tend to be much deeper than
the depth where sinkholes typically can affect people. Nonetheless,
in 1980 residents of the West Texas town of Wink awoke one
morning to find a 370-foot wide, 110-foot deep sinkhole
a couple of miles north of downtown. Geologists suspect
the sinkhole formed as a result of historic (and by today‘s
standards outdated) oil production practices in the area
whereby extractors pumped saltwater out from underneath
the surface and left a void that the above layer of earth
eventually collapsed into. A second, even bigger sinkhole
opened up nearby in 2002.
EarthTalk: I’m considering going for
a teeth whitening, but is this safe to do?
-- Clara Reid, Kent, Washington
experts warn that consumers should beware of the risks
of using stronger varieties of teeth whiteners containing
hydrogen peroxide. Hydrogen peroxide tends to be more
effective (it essentially bleaches the tooth enamel),
but it is a harsh chemical that can be poisonous if
© Jupiter Images
In the U.S.,
teeth whitening products are not regulated by the U.S. Food
and Drug Administration, as they are not classified as drugs.
As such, long term safety data doesn‘t exist for them.
But health experts warn that consumers should beware of
the risks of using stronger varieties containing hydrogen
peroxide. Hydrogen peroxide tends to be more effective (it
essentially bleaches the tooth enamel), but it is a harsh
chemical that can be poisonous if swallowed.
Europa, the official
website of the European Union (EU), cites studies showing
that bleaching teeth with hydrogen peroxide-based products
can “harm the surface of the teeth, making the enamel
more porous and leading to dents, scratches and loss of
minerals.” Europa further warns that it‘s important
for people to keep their tooth enamel in good condition
as it is “the protective, hard layer covering the
softer dentine inside the tooth” and “does not
regenerate.” The EU recommends people avoid tooth
whitening products with hydrogen peroxide levels higher
than a 1.5 percent concentration; most over-the-counter
varieties come in at about a 0.5 percent concentration level.
If the label on the product you are considering doesn‘t
indicate the concentration, it might be better to go with
one that has a more complete ingredients listing.
access teeth whitening solutions with higher concentrations
of hydrogen peroxide than are available over-the-counter;
as such a professional job in your dentist‘s office
will be more effective and last longer than the solutions
you can take home from the drug store. And while higher
concentrations of hydrogen peroxide might not be what you’re
looking for, dentists can apply it in more targeted ways.
If you do it yourself at home there is a greater chance
you will expose your gums and other parts of your mouth
to hydrogen peroxide or swallow more of it than you should.
As for maintaining
that bright white look, whether you did it yourself or had
it done professionally, your local drugstore or supermarket
no doubt carries a wide selection of toothpastes that claim
to whiten teeth. The ones which work the best contain—you
guessed it!—hydrogen peroxide, which can be irritating
if used day after day.
the health-minded home teeth whitener there are many less
harsh varieties of these toothpastes now on the market.
The website Skin Deep, a free online safety guide to cosmetics
and personal care products published by the non-profit Environmental
Working Group, lists Tom‘s of Maine Natural Antiplaque
Tartar Control Plus Whitening Toothpaste—which makes
use of all-natural hydrated silica, not hydrogen peroxide,
for whitening and stain removal—as one of the safest
kinds of whitening toothpastes out there today. Burt‘s
Bees Natural Fluoride-Free Whitening Toothpaste and CloSYS
Toothpaste for Teeth Whitening also get high marks from
Skin Deep for their natural, non-toxic ingredients. While
such products may not be “advanced” formulations
from a leading packaged goods conglomerate, your teeth and
body may thank you later.
Food and Drug Administration; Europa;
of Maine; Burt‘s
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